All he said was "why is your grandmother using a MAC?". He didn't say anything about someone using a mac being retarded (despite the common criticism and it being a bit childish), nor did he complain about her not knowing much about computers. And the gif is from doctor who but it doesn't show anything else or throw the show's reference's in anyone's face to classify it as more than a reaction gif.

A LOT of successful movies (300, X-Men Origins: Wolverine, The Ring), shows (Red vs Blue), and albums from musicians (Gorillaz, Nine Inch Nails, Coldplay, Christina Aguilera) have been made and/or edited using a Mac and/or Apple products, so I wouldn't necessarily jump to the conclusion that they're all retarded.

I'm not saying you can't hate or joke about Apple and/or Macs, as they have obvious flaws to them, but brainlessly hating on them just to hop on the bandwagon in a terrible attempt to impress your internet friends makes you look like a bitchy lemming.